DE2729244A1 - FELLING SILICIC ACID - Google Patents

Description

7170 FH

The invention relates to a hydrophobic precipitated silica and its use as a reinforcing filler in to Elastomer curable compositions.

Fillers are solid substances, mostly of inorganic origin and of various compositions, their particles
fine to coarse-grained and of various shapes and which are added to a chemical-technical product in order to improve certain properties

The invention relates to a hydrophobized precipitated silica which is characterized by

BET surface area m ² / g 110 + kO

Mean size of the primary particles

from EM recordings mn 15 - 22

Loss on drying according to DIN 55 921

after 2 hours at 105 ° C # <2.5

Loss on ignition (based on the 2 hours

substance dried at 105 ° C)

according to DIN 55 921 £ 5.5 + 1.5

pH value (in 5 # aqueous-methanolic suspension) according to DIN
53200 7.5 + 1.0

Conductivity (in k #iger wässrigmethanolischer slurry) / US (600

Tamped density of the non-vented

Substance according to DIN 53 19 ^ g / l 130 + kO

Water wettability £ 0.1

Carbon content % 2.5 + 0.6

Water absorption at 30 ⁰ C and 30 # RF # 1.2 + 0 _t k

at 30 ⁰ C and 70 # RH% 1.5 + 0.5

In a preferred embodiment of the invention hydrophobic precipitated silica can reduce the loss on drying from 2.5 to 0.0 ^. The conductivity of the invention hydrophobic precipitated silica can be from 50 to / US amount. The water wettability can be from 0 to 0.05.

• 08881/0474 ₂

717C FH

The invention also relates to a process for the preparation of the hydrophobic precipitated silica according to the invention, which is characterized in that In an original precipitation suspension, a precipitated silica with the following physical-chemical characteristics (characteristics obtained after separation from the precipitation suspension, intensive washing process with water and long-term drying of the hydrophilic precipitated silica):

BET surface area according to DIN 66 131 m ² / g I60 + kO mean size of the primary particles

from EM recordings mn 14-22

Loss on drying according to DIN 55 921

after 2 hours at 105 ° C 1 » 2.5-4.0

Loss on ignition (based on the 2 hours
substance dried at 105 ° C)
DIN 55 921 1> 3.5 + 1.0

pH value (in 5 # aqueous slurry) according to DIN 53 200 7.0 - 8.5

Conductivity (in 4 # aqueous

Slurry) / US (6OO

Tamped density of the non-vented

Substance according to DIN 53 194 g / l 1 ^ 0 + 40

S0_-salary (based on the 2 hours

substance dried at 105 ° C) # 0.3 Na ^ O content (based on the 2 hrs.

at IO50C dried substance) $ 0.3

a water repellent while maintaining an al Kaiischen pH, the mixture thus obtained is stirred, separated, dried for a long time, the product obtained 60 to 180 minutes, preferably 70 to 130 minutes for one Temperature from 200 to Ί00 C annealed and ground

808881/0474

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The original precipitation suspension of the hydrophilic precipitated silica can be obtained as follows:

1 part by volume of water is placed in a reaction vessel. 0.15 to 0.25 parts by volume of water glass solution (module SiO ₂ y ^Na 2 ° = 3.5 and 26 # SiO ₂ ) and 0.015 to 0.025 parts by volume of H ₂ SO ^ ( $ 6 #ig) are slowly added with stirring given to the template, an alkaline pH value is maintained in the mixture during the addition. After the addition of water glass and H “SO. the pH of the suspension obtained is in the weakly alkaline range.

As a hydrophobing agent, organosilicon compounds, which are suspended in the aqueous phase with the hydrophilic Precipitated silica are implemented, which have previously been used for such a reaction. Those are preferred the general formula

(R ₃ Si) _a Z,

where R is identical or different, monovalent, optionally substituted and / or polymeric hydrocarbon radicals, a1 or 2 and Z is halogen, hydrogen or a radical of the formula -OH, AOR, -NRX, -ONR ₂ , -SR, -OOCR, - 0-, -N (x) - or -S-, where R in each case has the meaning given above and X is hydrogen or has the same meaning as R. Examples of such organosilicon compounds are hexamethyldisilazane, Triraethylsilan, trimethylchlorosilane, trimethylethoxysilane, Triorganosiliylmercaptane as trimethylsilylmercaptan, Triorganosilylacylate as vinyldimethylacetoxysilane, Triorganosilylamine as Trimethylsilylisopropylamin, Trimethylsilyläthylamin, Dimethylphenylsilylpropylamin and Vinyldimethylsilylbutylamin, Triorganosilylaminoxyverbiiidunge as Diäthylaminoxytrimethylsilan and Diäthylaminoxydimethylphenylsilan, further Hcxamethyldisiloxan, 1,3-divinyltetramethyldisiloxane, 1,3 diphenyltetramethyldisiloxane and 1,3 diphenylhexamethyldilazane.

608881/0474 _k

7170 FH

-χ.

Other examples of organosilicon compounds that are used with in aqueous, alkaline phase-suspended, hydrophilic precipitated silica can be implemented within the scope of the invention, are dimethyldichlorosilane, dimethyldiethoxysilane, Dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, Vinylmethyldimethoxysilane and octamethylcyclotetrasiloxane and / or one each in the terminal units Dimethylpolysiloxanes containing Si-bonded hydroxyl groups with 2 to 12 siloxane units per molecule.

It can be a mixture of different organosilicon compounds be reacted with the precipitated silica present in the original aqueous precipitation suspension.

In a preferred embodiment of the invention, you can use dimethyldichlorosilane as a water repellent.

The OrganosjLiciumverbindungen that with the in aqueous, alkaline Hydrophilic precipitated silica present in the original suspension are preferably reacted in quantities from 5 to 30% by weight, based in each case on the weight of the with it precipitated silica to be converted is used.

The invention also relates to the use of the invention hydrophobic precipitated silica as a reinforcing filler in compositions curable to give elastomers on the Based on diorganopolysiloxanes. Thus, in a preferred embodiment, the hydrophobic precipitated silica according to the invention can be used in 1-component silicone rubber joint sealing compounds can be used.

It can also be used in organopolysiloxane elastomers curable at room temperature such as are preferably used, for example, in a two-component silicone impression compound.

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• 09881/0474

/ ι / υ - rf -.

* 27292U

According to the invention, the hydrophobic precipitated silica be used in hot-vulcanizing diorganopolysiloxane elastomers. This can be used, for example, as a cable insulation compound can be used.

As diorganopolysiloxanes, all diorganopolysiloxanes can be used that have hitherto been used as the basis for organopolysiloxane elastomers at room temperature (RTV) only slightly increased temperature (LTV) or high temperature (HTV) curable or hardening compositions were used or could be used. For example, you can go through the general formula

Z Si (R) -O- j Si (R) θΊ- Si (R) -Z ⁿ 3-n L * - ^{1 x} 3-n ¹¹

are reproduced, where R is identical or different, monovalent, optionally substituted and / or polymeric hydrocarbon radicals, Z a hydroxyl group, hydrolyzable Group and / or hydrolyzable atom or in the case of the presence of curable at only slightly elevated temperature Masses mean alkenyl groups, η 1,2 or 3 and χ a whole Number is worth at least 1.

Examples of carbon radicals R are alkyl radicals, such as Methyl, ethyl, propyl, butyl, hexyl and octyl radicals; .Alkenyl rusts, such as the vinyl, allyl, ethylallyl and butadienyl radicals; and aryl radicals such as the phenyl and tolyl radical.

Examples of substituted hydrocarbon radicals R are, in particular, halogenated hydrocarbon radicals, such as the 3t3i3-trifluoropropyl radical, chlorophenyl and bromotolyl radical;

and cyanoalkyl radicals, such as the beta-cyanoethyl radical,

Examples of substituted polymers (also known as "modified ¹ x inscribedable bare) and unsubstituted hydrocarbon radicals R are bonded to silicon via carbon PoIystyryl-, polyvinyl acetate, polyacrylate, polymethacrylate and polyacrylonitrile.

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At least the majority of the radicals R are present mainly because of the easier accessibility, preferably from methyl groups. Any remaining residues present R are in particular vinyl and / or phenyl groups «

In particular in the case of the presence of hates which can be stored with the exclusion of water and which harden to form elastomers on exposure to water at room temperature, Z are mostly hydrolyzable groups. Examples of such groups are amino, amido, aminoxy, oxira, alkoxy, alkoxyalkoxy (e.g. CH OCH ₂ CH ₂ O-), alkenyloxy (e.g. H ₂ C = (CH ₃ ) CO-), acyloxy - and phosphate groups. Acyloxy groups, in particular acetoxy groups, are preferred as Z, primarily because they are easier to access. However, excellent results are also achieved, for example, with oxir groups, such as those of the formula -ON = C (CH_) (C ₂ H _{5), as Z.} . .

Examples of hydrolyzable atoms Z are halogen and hydrogen atoms.

Examples of alkenyl groups Z are, in particular, vinyl groups.

Identical or different Z can be bonded to a Si atom be. ,.

Ee can be mixtures of different diorganopolysiloxanes be used.

The hydrophobic precipitated silica according to the invention becomes by mixing with diorganopolysiloxanes and optionally other substances at room temperature or only slightly higher Temperature, if appropriate after the addition of crosslinking agents, masses curable to give elastomers, in particular with exclusion Prepared masses that can be stored in water and harden to form elastomers upon exposure to water at room temperature. This Mixing can take place in any known manner, e.g. in mechanical mixing devices.

809881/0474 " ^{7 #} "

170 FH

The fillers used according to the invention are preferred in amounts of 5 to 50 wt .- ^, based on the total weight of the compounds that can be hardened to form elastomers, used for HTV organopolysiloxane elastomers can be used from 5 to 50 wt .- ^, will. With RTV organopolysiloxane elastomers from 5 to 35, preferably 5 to 25 wt .- ^ are used.

The diorganopolysiloxanes containing reactive terminal units are the only reactive terminal units Units with those with Si-bonded hydroxyl groups must have diorganopolysiloxanes in order to make them known per se Way to harden or to them in by the water contained in the air, optionally with the addition of further ^ Water to convert compounds hardening to elastomers, with a crosslinking agent, optionally in the presence of a condensation catalyst be implemented in a known manner. In the case of HTV diorganopolysiloxane elastomers, can correspond to high temperatures organic peroxides such as Bi.s-2.4-dichlorobenzoyl peroxide, Benzoyl peroxide, di-cumyl peroxide tert. Butyl perbenzoate or tert. Butyl peracetate used as a crosslinker will.

As hot-vulcanizing organosiloxanes, those can be used whose organic substituents consist of methyl, ethyl, phenyl, trifluoromethylphenyl 1 F CC ^ -H, - \ or trimethylsilmethylene radicals HCH ") _ SiCH - \, e.g. dimethyl, diethyl, phenylmethyl, Phenylethyl, ethylmethyl, trimethylsilylmethylenemethyl, trimethylsilylmethyleneethyl, trifluoromethylphenylmethyl or trifluoromethylphenylethylsiloxanes or copolymers of such compounds. In addition, the polymers can contain limited amounts of diphenylsiloxane, bis-trimethylsiiyimethylene-siloxane, bis-trifluoromethylphenylsiloxane units and also siloxanes with units of the formula FiSiO _ and R SiO, where R is one of the above radicals.

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Examples of crosslinking agents are, in particular, silanes the general formula

wherein R has the meaning given above for it, Z, an '; hydrolyzable group and / or a hydrolyzable atom and t is 3 or h . The examples given above for hydrolyzable groups Z and hydrolyzable atoms Z also apply in full to the hydrolyzable groups Z ¹ and the hydrolyzable atoms Z '.

Examples of silanes of the formula given above are methyl- ' triacetoxysilane, isopropyltriacetoxysilane, isopropoxytriace * -. oxysilane, vinyltriacetoxysilane, methyltrisdiäthylamino'oxysilane, Methyltris (-cyclohexylamino) -silane, methyltris (-difithylphosphato) -silane and methyltris (-ine thläthylketoximo) -silane

Instead of or in a mixture with silanes of the formula given above, polysiloxanes, for example, can also be used, which contain at least 3 Z 'groups or atoms per molecule, those which are not saturated by Z 'groups or atoms Silicon valences are saturated by siloxane oxygen atoms and optionally R groups. The best known examples of crosslinkers of the latter type are the polyethylene silicate with an SiO content of about ^ O wt .- ^, hexaethoxydisiloxane and methyl hydrogen polysiloxane

«08881/0474

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The best-known examples of condensation catalysts are tin salts of fatty acids, such as dibutyltin dilaurate, dibutyltin diacetate and tin (II) octoate.

Are in the reactive terminal units containing diorganopolysiloxanes as the only reactive, terminal units are those with alkenyl groups, the curing to elastomers can be carried out in a known manner with organopolysiloxanes, which contain an average of at least 3 Si-bonded hydrogen atoms per molecule, such as methyl hydrogen polysiloxane, in the presence of catalysts promoting the addition of alkenyl groups to Si-bonded hydrogen, such as platinum (iv) chloro acid. There are then at room temperature or only slightly elevated temperature (usually 50 to 80 ° C [curable (LTV) masses).

Finally, let us see another example of hardening. Elastomers those using polycyclic organopolysiloxanes in the presence of equilibration catalysts such as phosphonitrile chlorides.

It goes without saying that the compositions which can be hardened to give elastomers can be used. In addition to diorganopolysiloxanes, precipitated silica seeds according to the invention Crosslinking agents and crosslinking catalysts, where appropriate, usually usually or frequently in too Elastomer curable masses contain fillers used «Examples of such substances are fillers with a top

area below pO m / g, such as quartz flour, diatomaceous earth, further zirconium silicate and calcium carbonate, further untreated, pyrogenic silicon dioxide, organic resins such as polyvinyl chloride powder, organopolysiloxane resins, fibrous fillers such as asbestos, glass fibers and organic fibers, pigments, soluble dyes, fragrances, Corrosion inhibitors, agents that stabilize the masses against the influence of water, such as acetic anhydride, agents that delay hardening, such as benzotriazole, and plasticizers, such as dimethylpolysiloxanes which are end-blocked by trimethylsiloxy groups.

• 08881/0474. ₁₀ . .

7170 ro

The combination of physico-chemical properties of the hydrophobic precipitated silica according to the invention given leads to a highly effective reinforcing filler due to its excellent dispersibility. The equilibrium moisture content, which is significantly lower than that of the known precipitated silicas, has advantages during processing, for example in the case of pressureless vulcanization, which results in vulcanizates with fewer bubbles compared to the use of the known, hydrated precipitated silicic acid. The low electrolyte content in combination with the low moisture content ultimately leads to good electrical properties of the vulcanizates. In cold-curing silicone rubber sealing compounds, the hydrophobic precipitated silica according to the invention shows advantages for the shelf life of the uncured hate because of its low water content.

The manufacture, the physico-chemical data and the application of the hydrophobic precipitated silica according to the invention are explained and described in more detail using the following examples:

example 1

Production of the original precipitation suspension of a hydrophilic precipitated silica for the subsequent wet hydrophobization.

50.0 m of water are placed in a reaction vessel.

3 1

Slowly 9.2 nr water glass solution and 0.9 mr H_SO. added to the template with stirring, an alkaline pH value being maintained in the mixture during the addition. After the addition of water glass and H_SO. the pH of the suspension obtained is in the alkaline range.

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To characterize the hydrophilic precipitated silica, part of the suspension is filtered off, washed with little electrolyte, then in a drying cabinet at 105 C until the weight is constant dried and ground with the help of a pin mill.

The obtained hydrophilic precipitated silica has the following physico-chemical characteristics on:

BET surface according to DIN 66 131

Mean size of the primary particles from EM images

Loss on drying according to DIN 55 921 after 2 hours at IO50C

Loss on ignition (based on the ^{substance dried at 105 °} C. for 2 hours) according to DIN 55 921

pH value (in 5 5% aqueous slurry according to DIN 53 200

Conductivity (in k % aqueous slurry)

Tamped density of the non-vented material according to DIN 53

n » ² / g 155 mn 18-20 * 3.0 * 3.3 7.7 / ^US . 240 g / 1 140 * 0.22 0, 18

SO_ content (based on the substance dried for 2 hours at 105 ° C)

Na "O content (based on the 2 hours substance dried at 105 ° C)

Carrying out the determination of the electrical conductivity

A sample of k.0 g of silica is heated with 50 ml of deionized water in a 150 ml beaker and boiled for one minute while stirring. The suspension is then transferred to a 100 ml volumetric flask, cooled and made up to the mark with deionized water. After shaking, the measuring cell of the conductivity measuring device is first rinsed with the suspension to be measured and then filled or the measuring cell is immersed in the suspension. The electrical conductivity is read on the measuring device and the temperature of the suspension box of the measurement is determined

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Calculation ; The electrical conductivity is given in / US based on 20 ° C.

Example 2

Production of a product according to the invention obtained by wet hydrophobization hydrophobic precipitated silica

To 10 1 of an aqueous original precipitation suspension of the precipitated silica according to Example 1 with a solids concentration of 57.9 s / l while maintaining a pH-Vertes of the suspension of 8.5 193 g of dimethyldichlorosilane entered over a period of 30 minutes with intensive stirring. After a After a mixing time of 60 minutes, the precipitated silica, which is 25% coated with dimethyldichlorosilane, is separated off, dried at 105 ° C, tempered at 350 ° »and then ground.

separates, dried at 105 ° C, at 350 ° C for 2.0 hours

The resulting hydrophobic precipitated silica has the following physical-chemical characteristics:

Loss on ignition at 1000 ° C according to DI of which moisture at 105 ° C according to D pH value according to DIN 33 200
BET surface according to DIN 66 131 water wettability
conductivity
C content

Vasseraufnähme at 30 ⁰ C and 30 at 30 ⁰ C and 70

Tamped density of the non-vented material

according to DIN 53 194 g / l 130

Determination of the water-wettability of hydrophobic silicas

In the following analytical method wild the determination of the water-wettable Described proportions of hydrophobic silica.

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5 921 * 5.5 55 921 * 0.4 8.0 π » ² / β 89 * 0.05 yUS 160 i 2.2 RF 1.2 RF * 2.0

7170 ΠΙ

Execution of the determination ;

0.2 g of hydrophobic silica are placed in a 250 ml separating funnel with 50 ml of distilled water and 1 minute shaken with the help of a Turbula mixer at maximum speed.

After allowing the wetted parts to settle for a short time, 45 ml After gently swirling the suspension, drained it into an evaporation dish, evaporated it on a water bath and then dried at 105 ° C.

_ο . · Dry residue »100 4 . . . Calculation: _r = jo water-wettable

Weighed-in proportions

Determination of moisture absorption

When determining the moisture absorption, the maximum or time-dependent moisture absorption of silicas as a function of temperature and relative humidity certainly.

Execution of the determination :

A silica sample of approx. 2.5 U is weighed to the nearest 0.1 ng into a dry, tared weighing bottle and dried for 2 hours at 105 ° C. After cooling down, the weight is determined on an analytical balance. The open weighing jar with the sample is then stored in a clinical cabinet at a specified temperature and relative humidity. "It can then be either a moisture absorption time diagram or

the maximum moisture absorption can be determined, usually the determination takes place at

3O ⁰ C and 30 $> relative humidity 30 ⁰ C and 70 <f> relative humidity

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Calculation: g weight r 100 = $ moisture absorption

g weight *

* dried sample

Example 3

Use of a hydrophobic precipitated silica according to the invention in cold-curing 1-component silicone rubber compounds. In this example, the hydrophobic precipitated silica according to the invention according to Example 2 is used as a reinforcing filler and thixotropic agent Tested in a 1-component silicone rubber joint sealant (cold vulcanizing).

In the tests, the silica Aerosil 150 from Degussa and the commercial product HDK H2000 from Wacker are used Comparison tested in the same silicone rubber compound.

TJ

HDK H2000 is a highly dispersed silica, which by flame hydrolysis of volatile silicon compounds "and then is made hydrophobic by reaction with organosilanes. It is therefore dense on the surface with trimethylsilyl groups is documented and has the following physical-chemical characteristics:

BET surface area m '/ g 170 + 30

SiO ₂ content

Unpressed bulk weight

Moisture according to DIN 53 198 method A 2 hours at 105 ° C

Loss on ignition according to DIN 52 911 2 hours at 1000oc

pH according to DIN 53 200 in the k £ strength

Dispersion in water-methanol -1: 1 6.7-7.7

Mocker grit (DIN 53 580) adhering HCl

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mVg
Weight #
g / l 170 +
> 97
approx 90 Weight -i » <0.6 Weight # <2.5 Wt .- $
Weight-4 6.7 -
<0.020

Al ₂ O ₃ Fe ₂ O ₃ TiO ₂

Ι7Λ7Ο F * fr O, .05 O ₁ , 005 Weight O ₁ , 003 Weight 2729244 3 Weight < Weight < < <

Aerosil 150 is a pyrogenic silica with the the following physical-chemical characteristics:

BET surface area «NVg 150 + 50 Mean size of the primary particles ma 14th Loss on drying (DIN 53 198 / A)
(2 hours at 1O5 ° C7 0.5 Loss on ignition (DIN 52 911) (2 hours at
1000OC7 1 pH-Vert (DIN 53 200) (in 4 iger aqueous
ger dispersion) 3.6-4.5 SiO ₂ ♦ 1" 99.8 Al ₂ O ₃ * 0.05 Fe ₂ O ₃ * 0.003 TiO ₂ * 0.03 HCl 0.025 Mocker grit (DIN 53 58θ) i » 0.05 Bonetting behavior hydrophilic

* based on the substance annealed ^{at 1000 ° C. for 2 hours.}

The following recipe with acetate hardener is used as a basis:

68.4 parts by weight of dimethylpolydiloxane with hydroxyl end groups

Viscosity 50,000 cSt.

271 parts by weight of dirnethylpolysiloxane with trimethylsiloxyend-

group viscosity 1000 cSt

4.5 parts by weight methyltriactstoxysilane (crosslinker) 0.005 part by weight of dibutyltin diacetate plus silica to be tested '

16.-

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The incorporation of the silica takes place after ¹ "addition of the crosslinker in an evacuable planetary mixer.

The still pasty joint sealing compound or 7 days on the Air cured vulcanizate was then subjected to the following test:

a) Extrudability according to ASTM 2 ^ 52-69

b) Stability according to the hat method

c) Module at 100 # elongation according to DIN 53 5O4

d) Tensile strength according to DIN 53 50h

e) Elongation at break according to DIN 53 5O4

f) Tear strength according to DIN 53 515

g) Shore A hardness according to DIN 53 505

The results of these studies are shown below Table I summarized. Compared to the known pyrogenic hydrophilic silicas, Aerosil 150 and the hydrophobic silica HDK H2000 determine the following technical progress:

- Aerosil 150 can only be worked into the 1-component sealant up to 8 Jb · A higher degree of filling leads to
to a mass that is difficult to process · The level of mechanical data that can be achieved with a filling level of 8 * f> corresponds to the current state of the art.

On the other hand, with the silica according to the invention according to Example 2, a filling level of $ 20 becomes essential
A higher level of mechanical data is achieved, which meets the requirements placed on high-strength sealing compounds. The extrudability of the mass is completely reduced with this degree of filling. The storage stability is also good.

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vr. Zo

On the other hand, at a filling level of 20 %, the value level of the mechanical data of the commercial product HDK H2000, which represents the latest state of the art, is not comparable to that of the vuicanisates filled with the precipitated silica according to the invention. This applies in particular to the tensile strength and the elongation at break, which are both h5 $> below the corresponding values of the silica according to the invention. Only when the degree of filling is increased to $ 25 can the data generation for HDK H2000 be fully aligned.

Surprisingly, it was thus found that using only 20 ^ b of the precipitated silica according to the invention, a property profile that is in some cases significantly better (than $ 25> IDK H2000) can be achieved. The noticeably low manufacturing costs compared to hyrogenic hydrophobic silica open up additional application possibilities.

Table I.

Testing of a hydrophobic precipitated silica according to the invention , ^ em according to Example 2 in an I-component silicone sealant Prior art fumed silica.

Silicic acid type Type I

Storage stability;

Stability Extrudable- (llütchenj speed method) (g / rain)

Silicic acid according to example 2

Aerosil 150

HDK 112000

20th

20th

good Good

good Good

8.2 after 0 days 8.0 after 28 days

8 after 0 days

8 after 28 days

19 after 0 days 22 after 28 days

1 1 after 0 days f3n

9 after 28 days

- G0W .- / O, based on GcsamtniiscVm-τ / χ

3Q9831 / C

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ieseic acidet
Type yp Module 100 Tensile strength
speed fracture
strain Further-
tear
consolidate
speed Shore A
hardness (N / mm ² ) (N / mm) (*) (N / mm) silica
jera. Example 2 20th 4.6 45 780 16 18th ierosil 150 8th 3.0 10 400 2.5 20th TOIt H2000 20th 5.0 25th 430 15th 24 25th 6.0 45 400 18th 32
I.

Wt .- ^, based on the total mixture

Example 4

Production of a hydrophobic precipitated silica according to the invention obtained by wet hydrophobization. To 12 l of an original precipitation suspension of the precipitated silica according to Example 1 with a solids concentration of 57.9 g / l, while maintaining a pH of the suspension of 8.5, 175.6 Q dimethyldichlorosilane is added over a period of 30 minutes with vigorous stirring. After a subsequent mixing time of 60 minutes, the ^{precipitated silica coated} to 20 5 ° with dimethyldish.lorosilane is dried at 105 ° C., tempered at 35 ° C. for 1.5 hours and then ground. The precipitated silica obtained has the following physical-chemical characteristics:

Loss on ignition at 1000 C according to DIN 55 921

lavon humidity at I05 C according to DIN 55921

jH value according to DIN 53 200 3ET surface according to DIN 66 131

5.5

0.4 7.5 94

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Water wettability conductivity

C content

Water absorption at 30 ° C and 30 $ RH

at 30 ° C and

Tamped density of the non-ventilated material according to DIN 53 194

RF

US

0.06 92

2.1 1.3 2.0

137

Example 5

Use of a hydrophobic precipitated silica according to the invention in cable compounds based on organopolysiloxanes.

In this example, the erf indungsgeinässe hydrophobic precipitated silica according to Example is incorporated as a reinforcing filler in silicone rubber heissvulkanisierendon and tested on the electrical resistance of the vulcanizates produced therewith k.

Thanks to its excellent dielectric properties it takes place Hot-vulcanizing silicone rubber also used as a high-quality cable insulation material. As a reinforcing filler usually highly active fumed silica because of this their unity and favorable dielectric properties are used. It is known that the insulation properties continue can be improved if the fully vulcanized masses still undergo a longer tempering process (at least 6 hours) at higher temperatures Temperatures (around 200 C) are subjected.

The following recipe was used in the tests for this example worked:

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1OO parts by weight of diinethylpolysiloxane with trimethyl

siloxy end groups and a content of vinyl groups

40 parts by weight of silica

1.4 parts by weight bis-2.4 dichlorobenzoyl peroxide (50

as paste in silicone oil)

Vulcanization: 7 min at 130 ° C Tempering: 0 or 6 hours at 200 ° C Conditioning: 24 hours at 22 ° C and 80

humidity

rel. air

The results of the test in comparison with Aerosil 200, a pyrogenic silica from Degussa, are shown in FIG. As can be seen from the curves, with the inventive Surprisingly, precipitated silica achieve resistance values that are as good as those achieved with fumed silica, Furthermore, it has surprisingly been found that the silica according to the invention has the good electrical properties can also be achieved without the complex tempering process mentioned above permit. In addition to the more favorable manufacturing costs, this is another advantage of the precipitated silica according to the invention.

* Aerosil 200 is a flame hydrolysis of volatile silicon compounds Manufactured highly disperse silica, which has the following physical-chemical characteristics:

BET surface area

Mean gross of the primary particles tamped volume (DIN 53 194) compacted goods

m / g 1 200+ _v ,
ml / 100 g 1 12th
700 m.L / 100 g 000

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Loss on drying (DIN 53 Verf.A) 2 hours at 1O5 ° C

Loss on ignition (DIN 52 911)

2 hours at 100 ° C% by weight <1.5

pH value (DIN 53 200) in k #iger

aqueous dispersion Weight 3,6 - k, 3 SiO ₂ Weight > 99.8 Al ₂ O ₃ Weight <0.05 Fe ₂ O ₃ Weight <0.003 Weight <0.03 HCl Weight <0.025 Mocker grit (DIN 53 5δθ) 0.05

Claims (1)

717O FH Deutsche Gold- und Silber-Scheideanstalt formerly Roessler 600O Frankfurt am Main, Veißfrauenstrasse 9 Precipitated silica patent claims 1. Hydrophobic precipitated silica, characterized by BET surface area according to DIN 66 131 m ² / g 110 + kO Mean size of the primary particles from EM images mn 15 - 22 Loss on drying according to DIN 55 921 after 2 hours at 1O5 ° C% <2.5 Loss on ignition (based on the 2 hours substance dried at 1O5 ° C) according to DIN 55 921 £ 5.5 + 1.5 pH value (in aqueous-methanolic suspension of 5%) DIN 53 2OO / US 7.5 + 1.0 Conductivity (int% aqueous
methanolic slurry) W.
egg (öoo Tamped density of the non-vented
Substance according to DIN 53 194 130 + ho Water wettability % <0.1 Carbon content % 2.5 + 0.6 Water absorption at 30 ⁰ C and 30% RH % 1.2 + 0.4 at 30 ° C and 70% RH U5 + 0.5 2. Process for the production of the hydrophobic precipitated silica according to claim 1, characterized in that precipitated silica is added to an original precipitation suspension 809881/0474 ORIGINAL INSPECTH) 7170 FH with the following physical-chemical characteristics (characteristics obtained after separation from the precipitation suspension, intensive washing process with hater and long-term drying of the hydrophilic precipitated silica): BET surface area according to DIN 66 131 n> ² / e i60 + 40 mean size of the primary particles from EM recordings mn i4 - 22 Loss on drying according to DIN 55 921 after 2 hours at IO50 C # 2.5-4.0 Loss on ignition (based on the 2 hours substance dried at 105 ° C) DIN 55 921 $ 3.5 + 1.0 pH (in 5% aqueous slurry) according to DIN 53 200 7.0 - 8.5. Conductivity (in 4% aqueous slurry) yUS \ 6OO Star tap density of the non-vented Substance according to DIN 53 194 g / l i40 + 40 SO_ content (based on the 2 hours substance dried at 105 ° C) # \ 0.3 Na_O content (based on the 2 hours substance dried at 105 ° C) # \ 0 »3 adding a water repellent while maintaining an alkaline pH value, the mixture thus obtained stirred, the hydrophobized precipitated silica is separated off, long-term drying, the product obtained for 60 to 180 minutes, preferably 70 to 130 minutes at a temperature of Annealed and ground at 200 - 400 °. 3 · Use of the precipitated silica according to claim 1 as Reinforcing filler in compounds that can be hardened to form elastomers based on diorganopolysiloxanes. 608881/0474 717Q h, Use of the precipitated silica according to Claim 1 as a reinforcing filler according to Claim 3 in 1-component silicone rubber joint sealing compounds. 5 * Use of the precipitated silica according to claim 1 as Reinforcing filler according to claim 3 in silicone rubber cable compounds. PAT / Dr Ve-Eh 21 June 1977 809881/0474